1. Field of the Invention
The present invention relates generally to mechanical press machines and, more particularly, to a bed adjustment assembly including a piston-cylinder arrangement which enables micro-adjustments to be made to the shutheight parameter by utilizing a piston device having elastic tensile properties.
2. Description of the Related Art
Mechanical presses of the type performing stamping and drawing operations have a conventional construction comprising a frame including a crown and bed portion and a slide supported within the frame for reciprocating movement toward and away from the bed. The slide is driven by a crankshaft having a connecting arm coupled to the slide. These mechanical presses are widely used for a variety of workpiece operations employing a diverse array of die sets, with the press machine varying substantially in size and available tonnage depending upon its intended use. The availability of a diverse selection of die sets for installation into the press machines requires an adjustment capability that tailors the shutheight dimension to the particular configuration of press machine and die assembly.
One conventional press arrangement employs a slide configured for connection to the crankshaft by a connecting rod that is adjustable in length or which is connected to another device such as a connection screw that is adjustable in its spatial separation from the slide, thereby permitting adjustments to the shutheight dimension in order to accommodate various die sets. Adjustment mechanisms of the type employing an adjustable connecting rod or connection screw have typically been arranged such that the actuating mechanism is disposed within the slide, requiring that any shutheight adjustments be made only through changes in the position of the slide relative to the bed. In one such arrangement a plurality of connection screw assemblies configured with the slide may be adjusted simultaneously by means of a worm-gear arrangement, which is driven either manually or by means of an operator controlled motor. This adjustment procedure changes the position of the slide relative to each of the connection screws to thereby effect a change in the shutheight. However, the amount of slide displacement available from such screw-based arrangements is limited by dimensional considerations relating, for example, to the size of the screw, e.g., its longitudinal extent. Additionally, such arrangements provide a low order of efficiency in terms of their ability to make rapid changes in the shutheight, instead allowing more incrementally gradual changes as the screw needs to be sufficiently driven to produce the appropriate amount of slide-displacing rotational activity. The conventional strategy which relies upon making adjustments to the slide position to achieve shutheight variations is not always compatible with press machine configurations in which the crown area does not provide adequate space or support for housing the needed assembly of connection screws, for example. Moreover, adjustment mechanisms having a high part count such as the multi-screw arrangement are more susceptible to malfunction from parts failure, inhibiting efforts to reliably maintain the press machine.
In another proposed conventional configuration, an adjustment member extends between the crown and bed of the press machine and acts to adjust the gap therebetween by exerting a force on the crown, as disclosed in U.S. Pat. No. 4,502,379. Columns are provided at the four corners of the frame to support the crown, while elastic tie rods are arranged to extend through the columns from the crown to the bed to establish a supporting connection therebetween. Adjustment members in the form of a piston-cylinder arrangement are provided next to the support columns and extend between the crown and bed in the form of a columnar structure. Each piston-cylinder device operates in response to changes in its hydraulic pressurization to generate a force that acts upon the crown to vary its position, which is made possible by the tie rods since they are caused to be stretched within their elastic limits under the separating force generated by the piston-cylinder arrangement. The upward crown displacement and accompanying tie rod extension produce a change in the shutheight between the slide and bed. This configuration, however, has certain drawbacks; for example, housing the piston-cylinder assembly within the shutheight area between the crown and bed may create an obstruction that interferes with attempts by the operator to access the die set for servicing or other purposes.
In another proposed configuration there is provided an apparatus for adjusting the bed member of the press machine that employs an arrangement of piston rods connected to the corners of the bed member at an upper side thereof facing the crown. These piston rods extend upwardly into respective stationary cylinders which, at their upper ends, are fixed to the press frame. Adjustments are made to the bed position by varying the piston displacement. This arrangement, which is disclosed in U.S. Pat. No. 3,858,432, is likewise characterized by its placement of the adjusting mechanism (i.e., piston-cylinder assembly) in overlying relationship to the bed and interposed between the crown and bed. The piston rods in this configuration are required to bear the entire lifting burden in a relatively non-distributed manner at least in the lateral dimensions because of the primarily longitudinal strength profile typical of a piston device. This force distribution may introduce certain limitations with regard to the weight bearing capacity of the piston rods and hence the range of achievable shutheight variations.